Defect bound by equivalent matrices conjecture

Let HH be a complex Hadamard matrix, let d(H)d(H) denote its defect, and let 1H~|1\in\widetilde{H}| be the number of entries equal to 11 in a matrix H~\widetilde{H}. Two complex Hadamard matrices are equivalent when one is obtained from the other by the equivalence operations of Definition 1.3.

Defect bound conjecture. We have

d(H)max1H~,d(H)\leq\max|1\in\widetilde{H}|,

where the maximum ranges over all matrices H~\widetilde{H} equivalent to HH.

The claim seeks to bound the deformation-theoretic defect using the largest possible number of unit entries among equivalent representatives. The source presents it as part of a broader attempt to recover the defect from the statistics of these unit-entry counts; its resolution is not given.

Sources & referencesView supporting material

Primary source

Teodor Banica, “First order deformations of the Fourier matrix”, arXiv:1302.4153 (2013).

Additional references

2 papers in this index state this conjecture (2007–2013). The statement above is taken from the most recent of them; the others are arXiv:0707.1852.

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